This invention relates generally to electric motors, and more particularly, to a motor starting device.
At least some known electric motors include a start or auxiliary winding and a run winding. Either the start or run winding may be used to initiate rotation of a motor rotor. More specifically, when the start and run windings are energized, a geometric and time phase relationship between magnetic fields generated by the run and start windings, and the magnetization of the rotor, cause the rotor to begin rotating from a standstill condition. Once the rotor has sufficient torque to attain its normal running speed, the start winding is disconnected from the motor circuit.
Start and run capacitors are sometimes used to change the time phase relationship between magnetic fields generated by the run and start or auxiliary windings. If a run capacitor is connected in series with the start winding, rather than disconnecting the start winding once sufficient rotor torque is attained, the start winding may be utilized as an auxiliary run winding after motor start-up. More specifically, an auxiliary run winding facilitates improving motor efficiency and power factor. A motor starting switch may be used to control energizing and de-energizing the motor start winding or start capacitor. At least some known motors include a positive temperature coefficient resistor/over load (PTCR/OL) used to perform this switching function.
In at least some hermetic compressor applications, a separate PTCR/OL and run capacitor are externally mounted to the compressor housing. The PTCR/OL and capacitor are then electrically coupled to the motor circuit. Accordingly, the capacitor and PTCR/OL must be assembled separately, and as such manufacturing costs are increased. Additionally, over time, the electrical and mechanical connection between the PTCR/OL and capacitor may deteriorate when exposed to adverse conditions.